1. Field of the Invention
The present invention relates to a photoelectric conversion apparatus, and, more particularly, to a photoelectric conversion apparatus for use in an input portion of an information processing apparatus such as a facsimile machine, an image reader, a digital copying machine and an electronic blackboard or the like in which image information formed on the original document is read out by relatively moving the original document while closely bringing the original document into contact with a portion above a one-dimensional line sensor.
2. Related Background Art
Recently, an elongated line sensor having an equal-magnification optical system as a photoelectric conversion apparatus has been developed in order to reduce the overall size of a facscimile machine, an image reader and the like and to improve the performance of the same. Furthermore, in order to reduce the overall size and cost, there has been developed a photoelectric conversion apparatus of the type arranged in such a manner that the equal-magnification fiber lens array is omitted from the structure and light reflected from the original document is directly detected by a sensor via a transparent spacer such as a thin plate glass.
FIGS. 1A and 1B respectively are schematic views which illustrate a photoelectric conversion apparatus of the type described above disclosed by a group including the inventor of the present invention in "Nikkei Electronics" p.p 207 to 221, Nov. 16, 1987 (No. 434) and that disclosed in U.S. Pat. No. 4,924,282.
FIG. 1A is a schematic cross sectional view of a photoelectric device array for a conventional photoelectric conversion apparatus when viewed from the main scanning direction. FIG. 1B is a schematic plan view of the photoelectric conversion device array when viewed from the original document. FIG. 1A is a cross sectional view taken along line A--A' of FIG. 1B.
The conventional photoelectric conversion apparatus has been arranged in such a manner that a-Si:H (amorphous silicone hydride) is used to, by a simple process, integrally form, on a light transmissive insulating substrate 10, a photoelectric conversion device portion 1, a registering capacitor portion 2, TFT (Thin Film Transistor) portions 3 and 4, a matrix signal circuit portion 5 and a gate drive circuit portion 6.
On the insulating substrate 10, there are formed a first conductive layer 24 made of Cr, an insulating layer 25 made of SiN, a photoconductive semiconductor layer 26 made of a-Si:H, an ohmic contact layer 27 made of n.sup.+ a-Si:H and a second conductive layer 28 made of Al.
On the second conductive layer 28, there are, via an adhesive layer 9 and an electrostatic shielding layer 15 made of a light transmissive conductive material such as ITO, formed: a passivation layer 18 made of an organic material such as polyimide containing impurity ions in an extremely small quantity for the purpose of mainly protecting and stabilizing the surface of the conductor of the photoelectric conversion device portion 1 and the TFT portions 3 and 4; and a wear resisting layer 8 formed on the passivation layer 18 and made of microsheet glass or the like for the purpose of protecting the photoelectric conversion device and the like from the friction with original document P which is conveyed by original-document conveying rollers T.
The conventional photoelectric conversion apparatus thus-constituted has a light source S disposed adjacent to the light transmissive substrate 10 on the side opposing the original document P. Illuminating light L emitted from the light source S transmits the light through transmissive substrate 10 before the original document P is irradiated with it. Reflected light L' from it is received by the photoelectric conversion device portion 1. Optical information made incident upon the photoelectric conversion device portion 1 is converted into an optical current before it is registered as a charge in the registering capacitor portion 2. Then, the charge is transmitted to the matrix signal circuit portion 5 by the switching action performed by the TFT portion 3 before it is read out from outside.
FIGS. 2A to 2C respectively illustrate a method of manufacturing a conventional photoelectric conversion apparatus disclosed in Japanese Patent Laid-Open No. 1-128578, more particularly, illustrate a method of adhering a wear-resisting layer to the surface of the photoelectric conversion device.
First, as shown in FIG. 2A, a plurality of photoelectric conversion arrays are formed in the sub-scanning direction (direction Y shown in FIG. 2A), the photoelectric conversion array being constituted by forming the photoelectric conversion device portion 1 and the TFT portion 3 in the main scanning direction (direction Y shown in FIG. 2A) on a large-size glass substrate 50 to an extent of, for example, 1728 bits. Furthermore, a passivation layer 18 made of a polyimide resin is formed on the photoelectric conversion array. Then, as shown in FIG. 2B, an adhesive agent 19 made of an epoxy resin is applied to the substrate except for the contact electrode 17 in which a bonding pad is formed for the purpose of establishing an electric connection with an external circuit (omitted from illustration) so as to place the wear resisting layer 8 made of thin plate glass and having a light transmissive electrostatic shielding layer on the lower surface thereof on the above-described adhesive agent 19. Then, as shown in FIG. 2C, a pressing roller R is used to press the thin plate glass adjacent to the contact electrode portion 17 in the scanning direction while starting from the end portion of the thin plate glass 8 so that the thin plate glass 8 is caused to adhere to the surface of the photoelectric conversion device. Then, the adhesive layer 9 is hardened before the substrate is sliced along separation lines 19 so that the photoelectric conversion arrays are formed.
However, the above-described conventional photoelectric conversion apparatus encounters the following problems when its overall cost is required to be further reduced.
In order to reduce the overall cost of the photoelectric conversion apparatus, a method is employed in which the sub-scanning directional width of the light transmissible substrate on which the photoelectric conversion device portion and the like are formed is reduced. The photoelectric conversion apparatus of the above-described type is manufactured in such a manner that a plurality of photoelectric conversion arrays are simultaneously formed on the large-size light transmissive substrate before it is separated into each photoelectric conversion array so that individual array-shape photoelectric conversion apparatuses are formed. That is, by reducing the width of the light transmissive substrate on which the photoelectric conversion device portion and the like are formed, the number of the photoelectric conversion arrays which can be formed on the large size substrate can be increased. As a result, the cost of the photoelectric conversion array can be reduced.
In a case of the conventional photoelectric conversion apparatus in which the organic material such as polyimide is employed to form the passivation layer, it is difficult to reduce the cost by simply reducing the width of the substrate because of a problem of deterioration in the moisture resistance. The reason for this lies in that, since the organic material such as polyimide has a moisture absorbing characteristic or water permeability, water is, with time, introduced into the photoelectric conversion apparatus through its end portions of the substrate shown in FIG. 1A as water introduction areas, causing the semiconductor layer formed in the photoelectric conversion device portion or the TFT portion to be deteriorated. The conventional photoelectric conversion apparatus has been arranged in such a manner that the regions from the end portion of the substrate to the photoelectric conversion device portion and the TFT portion are enlarged so as to delay the time in which water introduced through the end portion of the substrate reaches the semiconductor layer of the photoelectric conversion device portion or the TFT portion. Thus, the margin enabling the moisture resistance of a practical level to be realized has been maintained.
Therefore, it is difficult for the conventional photoelectric conversion apparatus the passivation layer of which is made of an organic material to reduce the width of the substrate in terms of maintaining the practical performance. Therefore, it has been difficult to provide a photoelectric conversion apparatus the cost of which can further be reduced while maintaining the performance of the level which has been realized in the conventional apparatus.
On the other hand, it might be considered feasible to employ a method of reducing the cost by using an inorganic thin film material such as silicon nitride film or silicon oxide film displaying substantially no water permeability to maintain the moisture resistance of the photoelectric conversion apparatus and to reduce the width of the substrate.
However, in a case where the inorganic thin film material is used to form the passivation layer, there arise the problems shown in FIGS. 3A and 3B, which are the cross sectional views taken along line C--C' of FIG. 1B.
With the above-described conventional method of adhering the thin plate glass to the surface of the photoelectric conversion device, an end portion 20 of the thin plate glass 8 on the surface of which the light transmissive electrostatic is formed as shown in FIG. 3A strongly hits the passivation layer 18 and the impact generated in this case will break the passivation layer 18 made of the inorganic thin film. As a result, a crack 21 is generated in the passivation layer, causing the moisture resistance to be deteriorated. Furthermore, when the thin plate glass 8 placed on the photoelectric conversion device is caused to adhere to the above-described portion by pressure, the crack 21 deteriorating the moisture resistance will be generated in the passivation layer 18 made of the inorganic thin film due to the stress concentration taking place in the stepped portion in the photoelectric conversion device portion and the circuit portion or a hillock 28A excessively grown in the Al circuit portion 28.
If the crack is generated in the passivation layer, a fact that the following phenomena will take place has been confirmed:
(1) Water introduced through the crack will deteriorate the semiconductor layer of the photoelectric conversion device portion or the TFT portion. As a result, the S/N of the photoelectric conversion apparatus is deteriorated.
(2) Water introduced through the crack and impurities such as chloride ions (Cl-) contained in the adhesive layer will corrode the Al circuit portion due to a bias effect applied to the inside portion of the photoelectric conversion apparatus. Consequently, the Al circuit portion can be disconnected.
Therefore, the durability cannot be satisfactorily maintained simply by making the inorganic thin film material to be the passivation layer. As a result, there is a room to be improved for the purpose of further reducing the cost of the photoelectric conversion apparatus.